1. Field of the Invention
The present invention relates to a heat exchanger assembled without brazing, and to a mechanically assembling method in which adhesive is used to seal a combined portion between a tube and a core plate, which is effectively applied to a radiator for cooling car engine coolant.
2. Description of Related Art
Heat exchangers in which adhesive is used to seal the combined portion are known. According to these conventional structures, a supporting structure at the combined portion is such as shown in FIGS. 17A-17C, for example. That is, after both ends of a cylindrical tube 14 being inserted into a circular barring hole 16a of a core plate 16, the tube 14 is expanded so that outer peripheral surface of both ends of the tube 14 (the combined portion) are press fit with inner peripheral surface of the barring hole 16a of the core plate 16, thus, the tube 14 and the core plate 16 are integrated.
Next, adhesive 24 is potted at an air flowing side face (right side face of FIG. 17B) of the core plate 16 to seal the press fit combined portion between the tube 14 and the core plate 16. Thus, water leak from this press fit combined portion is prevented.
However, according to the result of study of tests with respect to a sample of above-mentioned mechanically assembled type heat exchanger in which the combined portion is sealed by potting the adhesive 24, it was found that a difficulty of sealing at the combined portion sealed by adhesive is caused by the following reason.
When the heat exchanger is under the working condition, a pressure inside the heat exchanger rises, thereby, the core plate 16 is deformed as shown in FIG. 18B. Two-dot chain line A in FIG. 18B shows the core plate 16 which is not effected by the inside pressure, and solid line B shows the core plate 16 which is deformed by the inside pressure. Since the inner peripheral surface of a barring hole 16a of the core plate 16 is press fit to both ends of the tube 14, in case that pressure is increased inside a tank chamber constructed by the core plate 16 and a resinous upper tank 12 (or lower tank 13), as shown in FIG. 18A, out of the core plate 16, a portion of the core plate 16 in a groove 16b side which is connected to the tank 12 (tank 13) by caulking is deformed toward the tank 12 (tank 13), for pressure receiving area in the tank 12 (tank 13) side is large.
Due to the above-mentioned deformation of the core plate 16, adhesive 24 potted on the air flowing side surface of the core plate 16 is effected by stretching stress. Under this stretching condition, since the intermolecular distance of the adhesive becomes large, intruding speed of any other molecule consisting of the fluid inside the tank (in case of radiator, engine coolant including anti-freeze ingredient and anti-corrosive ingredient, and so on) into the adhesive 24 increases.
Furthermore, when molar volume of the above molecular becomes decreased by the rise in inside pressure, the intruding speed of the molecule into the adhesive becomes more increased.
Thus, deterioration of the adhesive 24 itself proceeds, and cohesive destruction of the adhesive 24 and exfoliation of the bonded surface arise. As a result, sealing difficulty at the combined portion (being denoted as "a" in FIG. 18B) and the leak of the fluid inside tank (water leak) arise.
Especially, recently, for reducing cost and weight, reducing the thickness (t) of an aluminum alloy core plate 16 (for example, 0.8-1.2 mm) and replacing a cylindrically shaped tube with an oval tube (the ratio of long diameter to short diameter: about 2-5) are greatly required. Accordingly, rigidity of the core plate 16 is reduced and the deformation is likely to be increased, so, the sealing difficulty at the combined portion becomes remarkable.